A primary cancer is often followed by secondary bone tumors. Despite all medical advances, bone tumors cannot be healed as they generally occur spread-out and can hardly be treated surgically. The probability of bone metastases is larger than 96% in the case of multiple myeloma, between 65% and 75% in the case of cancers of the breast and prostate, and between 30% and 50% in the case of cancers of the lung, kidney, cervix and bladder. Systemic chemotherapies have hardly any effect. Initial successes have been achieved using therapeutic antibodies. However, when therapeutic antibodies are used, there is the problem that they are mostly directed against targets which are only present on proliferating tumor cells. Generally not detectable are non-proliferating tumor cells in the blood circulation and latent metastases.
There is a close relationship between the occurrence of the bone matrix proteins osteopontin (OPN), osteonectin (ON) and bone-sialoprotein II (BSP) in the primary tumor on one hand, and the later occurrence of secondary blastomas of the bones on the other hand. The cells of an osteotropic metastasizing primary tumor nearly always express significant amounts of BSP or OPN (I. J. Diel et al., Clinic Cancer Res, 1999, 5:3914; A. B. Tuck et al., J Mammary Gland Biol Neplasia, 2001, 6:419; P. S. Rudland et al., Cancer Res 2002, 62:3417; D. Agrawal et al., J Natl Cancer Inst, 2002, 94:513; D. Waltregny et al., J Bone Miner Res, 2000, 15(5):834; A. Bellahcène et al., J Bone Miner Res, 1996, 11:665; D. Waltregny et al., J Nat Cancer Inst, 1998, 90:1000; A. Bellahcène et al., Int. J. Cancer, 1996, 69:350; WO 02/100901 (Immundiagnostik AG), WO 02/25285 (Smith et al.)).
BSP is a phosphorylated glycoprotein with a relative mass of about 80 kDa in SDS-PAGE. The cDNA for BSP codes for a peptide sequence of about 33 kDa (L. W. Fischer et al., J Biol Chem, 1990, 265:2347; U.S. Pat. No. 5,340,934 (Termine)). It represents about 10% to 15% of the non-collagen proteins in the bone matrix, and it is normally expressed by cells that are involved in the formation of dentine, bone and cartilage, such as osteoblasts, developing osteocytes, hypertrophic chondrocytes, odontoblasts and cementoblasts. As an adhesion molecule, BSP supports the attachment and spreading of osteoblasts and osteoclasts on the bone tissue matrix. The switching-off of the BSP-gene in knock-out mice did, however, not lead to a visible disruption of skeleton formation. However, BSP has been attributed a role in bone microcalcification and bone colony formation of tumor cells (V. Castronovo et al., Int J Oncol, 1998, 12:308; A. Bellahcène et al., Int J Cancer, 1996, 69:350).
Free BSP is bound with high affinity by complement factor H in body fluids. There are many antibodies against BSP peptide structures, recombinant BSP and BSP isolated from bone, which do not recognise and bind BSP in serum (L. W. Fisher et al., Acta Orthop Scand Suppl 1995, 266:61; J. T. Stubbs (III) et al. J Bone Miner Res, 1997, 12(8):1210). The 150 kDa large factor H molecule most likely encloses the BSP molecule in such a way that these antibodies cannot bind. Trophoblasts and BSP producing tumor cells are therefore also protected from an attack by the immune system (N. S. Fedarko et al. J. Biol. Chem., 2000, 275, 16666-16672; WO 00/062065). The heavy glycosylation of BSP may also play a role in this observation. Furthermore, BSP may bind through its RGD sequence (arginine-glycine-aspartic acid) to alpha(v)beta(3) integrin receptors on the cell wall. Thus, BSP is further involved in the adhesion, dissemination and orientation of the endothelial cells and the angiogenesis around a tumor (A. Bellahcène et al. Circ Res. 2000, 86(8):885-91). These properties make BSP, alongside OPN and ON in the family of non-collagen integrin receptor binding glycoproteins, a starting point for medicaments of all kinds (U.S. Pat. No. 5,780,526; U.S. Pat. No. 5,767,071; U.S. Pat. No. 5,792,745; U.S. Pat. No. 5,989,383; U.S. Pat. No. 5,773,412; U.S. Pat. No. 5,849,865).
There have been attempts to inhibit through RGD-antagonists the binding of BSP to the vitronectin and integrin receptors of the tumor and endothelial cells (U.S. Pat. No. 6,069,158; U.S. Pat. No. 6,008,213; U.S. Pat. No. 5,849,865; van der Pluijm et al., Cancer Res., 1996, 56, 1948-1955). EP 1 084 719 (DePuy Orthopaedics Inc.) describes BSP an active agent for supporting the repair of damaged bone and connective tissues. WO 94/11310 (Alfa-Laval Agriculture Intern. AB) discloses a BSP-binding protein from Staphylococcus aureus for a treatment of infections and inflammatory diseases of the bone. WO 02/100899 (Armbruster Biotechnology GmbH) discloses an active ingredient against bone metastases based on antibodies against BSP. WO 00/36919 (Univ. Virginia Patent Found.) describes regulatory elements for control and inhibition of BSP expression in tumor cells and connective tissue cells. Finally, EP 0 020 789 (DKFZ) discloses an inhibition of cell migration and bone metastasis formation by antisense-oligonucleotides (quod vide Adwan-Hassan et al. in Cancer Gene Therapy, 2003:1; Intern J Oncol, 2004, 24:1235-1244; Proc Am Assoc Cancer Res Ann, 2003, 44:56). WO 2006/036550 (Trustees of the Univ. of Pennsylvania; published after the priority date of this application) further describes vaccines on the basis of Listerium and fusion proteins of listeriolysin and CD8+-T-cell epitopes (Her-2) for a treatment of osteotropic tumors and carcinoma.
Therefore, it has been examined what causes a primary tumor, which can normally be surgically removed, to produce metastases and how bone metastases may be prevented and what is needed for their treatment or eventual cure. In previous attempts, it proved disadvantageous that a therapy based on antisense oligonucleotides or antibodies, when effective at all, can only be maintained effective for a limited period. There is not only a problem of dose and application, but also due to the development of autoantibodies against the therapeutic immunoglobulins and regulatory nucleotides. One should further not forget that the body contains natural endogenous BSP so that an immune reaction against endogenous BSP is inhibited. On the other hand, prophylaxis or a direct treatment of bone metastases must be carried on over very long periods in order to be potentially successful. The danger of an occurrence of bone metastases will last for decades after a treatment of a primary osteotropic tumor. Thus, there is a need for a therapeutic composition that sustainably prevents a colony forming and development of bone tumors, and fights any existing bone metastases.